The Protectoseal Series No. 8540H, End-of-Line Pressure / Vacuum Conservation Vent, is intended for use where both pressure and vacuum relief are required. The pallets in the vent housing allow intake of air and escape of vapors as the tank normally breathes in and out. Pallets open and close to permit only that intake or outlet relief necessary to remain within permissible working pressures and avoid damage to the tank. Reduces cost evaporation losses.